In relatively large office buildings, including hospitals, it is beneficial to be able to transport various materials or articles from one location to another with maximum efficiency. To accomplish such an objective, conveying systems have been developed which include tracks and vehicles which move along the tracks. The vehicles are designed for receiving and holding small articles which are transportable from one station located near one section of the track to another station located near another section of the track. Such vehicles are often referred to commercially as electric track vehicles (ETV), automated guided vehicles (AGV), or electrified monorail systems (EMS). The vehicles are typically propelled by one or more AC or DC electric motors, and derive their energy from on-board batteries or by electrified collector rails that run continuously along the track followed by the vehicles.
From the standpoint of control strategies, such automated conveyance vehicles can be entirely self-sufficient (i.e., determining autonomously when to start, stop, slow down, turn, back up, etc., based on external stimuli, time, distance or other factors) or, alternatively, such a vehicle may be entirely under the direction of a controller that is not part of the vehicle itself. A common arrangement is a combination of the above two strategies where each vehicle has a predetermined control capability but the vehicle is also in continuous or periodic communication with at least one external controller that provides traffic management, job assignments and other high level functions.
A common difficulty with such automatic conveying vehicles occurs when one such vehicle experiences a malfunction during transit, thereby causing the vehicle to stop for an extended period of time. In such cases, maintenance personnel often encounter difficulties in correcting the malfunction due to a "pile-up" of other vehicles behind the vehicle experiencing the malfunction. That is, one vehicle travelling along a route used in common by a plurality of conveyance vehicles stops and additional vehicles trying to traverse the same route queue up behind the first vehicle, each stopping by means of, for example, a bumper switch or other form of obstruction detection. In such cases, to gain access to or correct the malfunction at the front of the vehicle pile-up, substantially all the vehicles in the pile-up must be moved back a short distance, particularly if the vehicles are in direct contact with one another. One well known way of accomplishing this has been applied to electric track vehicles in the form of a three position toggle switch mounted somewhere on each vehicle such that each such switch is accessible by trained maintenance personnel. Commonly, the switch has three positions, two of which are maintained (i.e., the switch will remain in the position when switched) and the third being momentary (i.e., the switch will not remain in the position without the continual application of force). In this switch embodiment, one of the maintained positions is the position which enables the vehicle to operate in its usual fashion. A second maintained position for the switch allows the vehicle drive motor to be manually shut off, and thereby overriding all other control means such that the vehicle stops indefinitely. This second position is useful if a maintenance person wants to disable a vehicle while he performs work in its vicinity, or if the vehicle controls have failed in such a way as to leave the motor running even though the vehicle cannot move. The momentary third switch position reverses power to the vehicle motor so that it runs in reverse. This position can be used to back a vehicle away from a pile-up. The switch is typically spring loaded away from this position to prevent the possibility of inadvertently leaving the switch in the reverse position, a position which can potentially cause head-on collisions between vehicles.
There are several shortcomings to using a simple toggle switch as above for manually overriding control of such conveyance vehicles. First, the switch is often mounted toward one side of the vehicle and may be difficult to reach if that side of the vehicle is facing, for example, a nearby wall. Second, the momentary action of the switch for back-up requires that manual contact with the switch be maintained while the vehicle is backing away from, for example, a pile-up. Often, a maintenance person is perched atop a high ladder, clinging hazardously to the walls of a vertical shaftway in a multi-story building, or in some other awkward location where maintaining contact with a moving vehicle is dangerous. The fact that the switch is usually mounted in a relatively inconspicuous location so that it is out of sight and temptation of users of the conveyance system serves to exacerbate the problem. Third, when the vehicle does move in reverse, it typically does so at full speed and full power. This abrupt movement further compounds the difficulties of maintaining manual control and adds to the hazard described above.
It would be advantageous to provide a simple means for taking control of such automated conveyance vehicles on a temporary manual basis without the foregoing disadvantages. That is, it would be advantageous for a maintenance person to be able to easily control each such vehicle by directing the vehicle to stop (temporarily or indefinitely), move backwards or operate normally using, substantially, existing vehicle components such as a bumper switch.